A polyimide resin, which is an insoluble and nonmeltable resin having ultrahigh heat resistance, is widely used in heat-resistant state-of-the-art materials for automobiles, aircrafts, spacecrafts, and the like, and electronic materials, such as insulating coating agents, insulating films, semiconductors, electrode protection films of TFT-LCD, and the like, because it has excellent properties, such as heat oxidation resistance, heat resistance, radiation resistance, low-temperature characteristics, chemical resistance, and the like. Recently, it is used in a transparent electrode film, and the like by surface-coating or containing a conductive filler in a film and marking material, such as optical fiber or liquid crystal alignment layer.
However, a general polyimide resin is colored brown or yellow because of its high aromatic ring density so that it has low transmittance in the visible light range and comes in some colors like yellow thereby reducing light transmittance with the result that it is difficult to use it in applications requiring transparency.
For this reason, there are diversely efforts to improve a color and a transmittance of a polyimide film, but there are two aspects as the results of the above efforts, that is, a heat resistance is reduced in proportion to the improvements of color and transmittance of film.
Furthermore, a transparent film having high heat resistance as well as a diversification of function is required for applications as various electrical and electronic materials applied with a polyimide film.